I have a copy of ISIRI-3342 standard (a scanned version that I found
somewhere), where the character on code position 0xA4 is explicitly
called RIAL SIGN. And the shape is simply the word "rial", written out
(in Arabic, of course). Your table says: CURRENCY SIGN (mapped to
U+00A4).

RIAL SIGN cannot be mapped to a single Unicode character so mapping to
CURRENCY SIGN would be more practical. But if 0xA4 was used as a Rial
sign and rendered "rial" in existing software and documents, mapping
it to CURRENCY SIGN would cause loss of information.